Process for manufacture of aviation gasoline



Patented May 2l, 1946 bBalCn HOOlTi PROCESS FOR MANUFACTURE OF AVIATION GASOLIN Walter A. Schulze and Carl J. Helmers, Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Application December 11, 1943, Serial No. 513,928

5 Claims.

'I'his invention relates to the production of high octane hydrocarbon fuels by the catalytic conversion of hydrocarbon oils. More specifically the invention relates to the production of aromatic hydrocarbon concentrates substantially in the gasoline boiling range and valuable for aviation gasoline stocks and/or as sources of high purity aromatic hydrocarbons.

In one specific embodiment this invention involves the catalytic conversion of gasoline or naphtha type hydrocarbon charge stocks to effect a high degree of aromatization, and the catalytic treatment of selected fractions of the normally liquid products containing the aromatic compounds to accomplish the removal of deleterious impurities and/or to improve the quality of said fractions for use in aviation gasolines or as feed stocks for the segregation or synthesis of valuable aromatic compounds,

The production and recovery of aromatic hydrocarbons from petroleum or other hydrocarbon fluids are of importance in supplying benzene, toluene, ethylbenzene, cumene and other compounds for a variety of blending and synthetic purposes. Another important use of hydrocarbon mixtures containing high concentrations of aromatic compounds in the gasoline boiling range is for the production of aviation gasoline blends of high octane number and superior rich mixture rating.

'I'he utilization ci' aromatic gasoline fractions in aviation gasolines not only requires high concentrations of aromatics in the blending stocks to impart the desired combustion characteristics, but also limits to low values the concentrations of undesirable hydrocarbon types which impair the blending octane ratings of the aromatics-rich fractions. Furthermore, the reduction or in some cases the substantially complete removal of nonhydrocarbon impurities such as sulfur compounds may be desirable in order to improve the quality of the aromatic blending stocks.

It is an object of the present invention to furnish a method for the production of aromatic concentrates and/or aromatic gasoline blending stocks suitable for the above-described uses.

It ls a further object of this invention to furnish a method for the catalytic conversion of selected liquid hydrocarbon feed stocks to gasoline stocks of unusually high aromatic content and relatively free of undesirable hydrocarbon types and non-hydrocarbon impurities.

Another object of this invention is the provision of a method for the production of blending stocks for aviation gasoline of superior rich mixture rating.

(Cl. 26o-673.5)

Still another object of this invention is to provide a process for the production of aromatic gasoline blending stocks of low olen and sulfur content by the catalytic treatment of selected portions of the products of catalytic aromatization and/or cyclization treatments.

Oher objects and advantages of the invention such as the production of superior aviation gasoline stocks from conventional reflnery gasolines or naphthas will be apparent from the following disclosure.

'I'he figure is a diagrammatic illustration of one form of apparatus in which the process of our invention may be practiced. It is to be understood that this flow diagram is diagrammatic only and may be altered in many respects by those skilled in the art and yet remain within the intended scope of our invention.

We have discovered that the production of aromatic gasoline stocks from various types of liquid hydrocarbon feed stocks may be accomplished by catalytic conversion under conditions yielding aromatic compounds which may be segregated with only minor proportions of other hydrocarbon types. We have further discovered that the aromatic concentrates produced by the said catalytic conversion may be substantially improved in quality by catalytic treatment under polymerizing conditions. We have also discovered that while conventional clay treatment is not suited to the purification of such aromatics-containing stocks. it is a highly desirable adjunct to our catalytic polymerization in that the prior removal of dienes and other tar forming constituents greatly prolongs catalyst life in the subsequent purification step. This secondary catalytic treatment effects desirable reduction in the olen and sulfur contents of the aromatic gasoline fractions Without involving the aromatic compounds in undesirable side reactions. In this manner the rich mixture blending rating and stability of the aromatic gasolini fractions are increased with negligible volume losses in treatment.

In addition, Lie aromatic concentrates produced by the process are improved for further processing to yield pure compounds or synthetic derivatives thereof. Principal by-products of the secondary treatment are often suitable for recycling to the primary catalytic conversion producing aromatics.

We have also found that the utility of catalytic aromatization reactions has been greatly extended by our secondary catalytic treatment of the crude aromatics-containing distillates. This secondary treatment over catalysts such as silicaalumina compositions greatly improves the richmixture rating of the product streams. Thus STC blending values as measured on blends containing 25 per cent of aromatic stocks with an added 4 m1. of lead tetraethyl fluid often show improvement in quality equivalent to from 2 to 4 ml. of TEL in S reference fuel. It is well known that heretofore in order to prepare high quality aromatic distillates severe conditions of catalytic cracking were required often involving multiple catalytic cracking operations utilizing the eiiiuent from one pass as the feed to the succeeding operation. Such operations often result in the conversion of as much as 50 per cent of the original feed stock to light gases. Such processes are not only costly from the standpoint of low yields on original feed and high catalyst regeneration costs; but also in view of the plant equipment involved in carrying out multiple pass operations. Thus in a three-pass cracking process, the catalyst cases might be arranged in series or the material from each pass may be collected intanks for subsequent treatment in a single catalytic reactor. In the first instance the equipment required is ex cessive in view of the volume oi product and in the second instance the time required to produce a given volume of product is economically unattractive. As a partial solution to these well recognized problems, careful selection of feed stocks has been resorted to in an effort to produce high qualityV products without excessive cost in equipment and time.

The present process obviates to a large extent the necessity for multiple-pass catalytic cracking operations by increasing the rich-rating through a novel treating operation carried out subsequent to a single-pass catalytic cracking step. Economy of feed stock consumption is also realized since it is now possible to produce a highquality aromatic-containing distillate with less severe crackingconditions for a given 3-C rating. Another important advantage of the present process is that the range of operable feed stocks has been greatly extended. Thus certain ria-ph thas which previously were rejected because of low-quality products produced at conventional cracking depths can now profitably be employed due to the exaltation in quality resulting from the present invention as herein described.

In the following description, one method of operating our process will be speciilcally disclosed. It is understood, however. that while this is representative in general of the operation, minor variations and departures may be necessary in adapting the process to the various conditions within the scope of our invention.

In the attached drawing a suitable charge stock, such as a polyform gasoline having a high carbon to hydrogen ratio, is withdrawn from a tank i into a line 2 where it is admixed with recycle stock from a line 56 and steam from a line 3 immediately ahead of a heating coil 4. The ei'iluent from the heater, having been raised to the desired temperature level of about 1100- l200F., is charged directly to a catalyst case 5 which is filled with a solid adsorbent type catalyst such as bauxite and in which conditions of temperature, pressure and contact time are selected so as to result in the formation of a maximum amount of aromatic compounds. I The hot eiiluent vapor from the catalytic cracking step is discharged through a line 8 and 'a heat exchanger 'I and a line 8 into a separator 8 where the condensed steam is continuously removed through a line i4 and the light hydrocarbon material is conducted via a lino H. a

compressor i2, and a line i3 to a high-stage accumulator I4. The pressure on the accumulator is maintained at a level high enough to eiect further condensation of water which is removed via a line l5, but not high enough to liquify the normally gaseous hydrocarbons. The compressed gas ows via a line i5 to a stripping column I1 where the C5 and heavier components are removed with the aid of the stripping action of the.

200-350 F. hydrocarbon fraction entering the top of the tower from a line 45. The overhead gases comprising C4 and lighter hydrocarbons are conducted to a vapor recovery system by way of a line i8. The fat stripping liquid leaves the column through a line I9 and is added to the main product stream ina line 20. The condensed hydrocarbon material in separator il is withdrawn through line 20 andyis reheated in heat exchanger l and subsequentlyiashed in a tower 2|. The unvaporized high-boiling hydrocarbons are discharged via a line 22 into a recycle transfer line 52 while the vaporized product stream is passed through a line 23 into a clay tower 24. The claytreated vapors are then discharged-by way of' a line 25 into an efficient The overhead fraction from column 26 which is rich inbenzene and olefinic hydrocarbons and which includes material boiling from C5 components to 200 F. is now treated separately from the main products stream. The 20o F. endpoint material is conducted through a, line 21 to a heater 28 where the temperature is raised to a suitable value of about 400 F. under sufficient into a line 42.- a

pressure to maintain substantially liquid phase conditions. The hot liquid is then discharged directly into a catalyst case 29 which is filled `with the preferred silica-alumina polymerization catalyst, and wherein polymerization reactions occur. The eiiluent from this polymerization treatment is permitted to vaporize in a line 420 as the pressure is reduced and resulting vapors are discharged into a fractionator 3i. An overhead fraction of F. end-point is transferred to motor fuel storage via a line 32. The kettle product from column 3l containing benzene, oleand some high-boiling alkylbenbeing charged .to a column 35 vla a line 83 and the remainder is returned to the recycle transfer line 52 by a line 34. From column 35 a benzene concentrate is taken` overhead through a line 36 to storage while the kettle product containing high-boiling aromatic material and olenic polymer. is returned through a line 31 to the recycle transfer line 52 for further processing.

The kettle product from the operation of column 26 and which contains the aromatic homologs boiling above benzene is transferred via a line 88 to a fractionator 39 where a 200350 F. overhead cut is made while the heavy ends are discharged via a line 40 into the recycle transfer line 52. The main product stream is conducted via a line 4I to a heater 48 where the temperature is raised to about 450 F. under sumcient pressure to maintain substantially a liquid phase condition. A portion of the product stream in liney 4l is continuously diverted condenser 43 and a redux accumulator 44. A portion of the accumulator liquid is utilized as reflux for column 89 and the remainder is transferred via line 45 for use as stripping liquid in the operation of column I1. The eiiluent from heater 48 is passed directly into a catalyst caso 4.1 which is filled with the pre- :erred silicaeluminc Polymerization ammunition.y

finie polymer zenes is divided; part Subsequent to a polymerization treatment therein, the eluent stream is vaporized by pressure comprising high-boiling polymer and aromatics is discharged via a line in the recycle transfer line 52.

In the operation of our invention according to this specific embodiment, kettle products from the operation of fractionating columns 2|, 3 I, 35, 39 4 and 48 are collected in recycle transfer line 52. In order to prevent an undue accumulation of high-boiling refractory material and to provide for disposal of sulfur compounds, a portion of the recycle stock is continuously removed from the system via a line 53 while the remainder is passed through heat exchanger 1 and vaporized in a tartrap 54. The non-volatile oil, tar and high-boiling sulfur compounds are discarded through a line 55 while the vaporized recycle stock is added to the fresh feed in line 2 by means of line 56.

'Ihe above specic embodiment of our process results in an exceptionally high yield of alkylated benzene derivatives as is attested by the interdependence of the catalytic cracking and treatingsteps. Since ordinarily the production of benzene is in excess of the volume that can be used in aviation gasoline blends, the excess benzenecontaining product stream from column 3| is recycled to the catalytic cracking operation and thereby affects the aromatics equilibrium in favor of alkylated benzene derivatives. In addition recycle products particularly from columns 3|, 49 and 35 furnish high-boiling olefinic polymers which are easily converted to benzene derivatives in the catalytic cracking step thereby increasing the. overall aromatics yield from a given volume of fresh feed.

An alternative operation 'may involve the catalytic treatment of a full range clay treated sta.- bilized stock. Thus, fractionator 26 may be used to cutout the C5 to'150 F. fraction and a full range overhead stock of about 150 to 350 F. may be produced in fractionator 39. This mode of operation affords economy of treating equipment since reactor 41 is then utilized in treating the total product and fractionator 49 can be employed in preparing a benzene-containing aviation blending stock. However, in many instances partial or complete segregation of the benzene fraction may still be desirable.

Another mode of operation may be employed in those instances where low sulfur selected feed stocks are available. Under such conditions the clay-treated 200-350 F. product stream will be low in both sulfur and olens and may not require further treatment. Under such conditions the fraction from column 39 constitutes a finished product-with the elimination' of heater 4B, reactor 41 and fractionator 49. However, treatment vof the light product stream from column 26 is mandatory, as shown, because of its high olefin content. I

The process of this invention can utilize a wide variety of feed stocks including straight-run and cracked gasoline, virgin and cracked naphthas and gas oil. However, in the production of aromatic distillates rather severe operating conditions are necessary when straight-run feed stocks and the heavier naphthas and gas oil. The preferred feed is a thermally or t `generally not bein excess of 10 per cent by weight,

catalytically cracked'gasoline with a restricted boiling range of about 150 to 400 F. and having a high carbon to hydrogen ratio.

'Ihe catalyst employed in the aromatization stage of this process is preferably an alumina base material which may be of natural or synthetic origin. The natural mineral bauxite is a preferred catalyst although other catalysts of suitable activity and properties may be used such as synthetic alumina promoted with minor proportions of other metal oxides.

Aromatiz'ation over the preferred bauxite catalyst is preferably carried out at temperature ranging from about 1050 to about 1250 F. Moderately superatmospheric pressures are recommended such as those extending from atmosphericto about 200 pounds per square inch. In many instances it may be desirable to employ a -diluent such as steam to aid in temperature control.

In the aromatic purification stage of the process which is a feature of the present invention, a synthetic gel type catalyst is employed. These catalysts are broadly referred to as silica-metal oxide compositions, but it is important to define vfurther the origin, physical structure and chemical composition in order to differentiate the catalysts active in the present process fromA naturally occurring minerals which containl some of the 'same components.

In general the preferred catalysts are prepared by first forming a hydrous silica gel .from an alkali silicate and an acid, washing soluble material from the gel, treating or activating the gel with an aqueous solution of a suitablemetal salt, and subsequently washing and drying the treated material.

is selectively adsorbed by the hydrous silica and is not removed by subsequent washing.

The silica-alumina type catalyst preferred in the treating stage of this process is prepared by treating a wet or partially dried hydrous silica.'

gel with an aluminum salt solution, such as a solution oi aluminum chloride or sulfate, and subsequently washing and drying the treated material. However, catalysts of a very similar nature but differing among themselves as to one or more specific properties. may be prepared by using a hydrolyzable salt of a, metal selected from group IIIB or from group IVA of the periodic system, and may be referred to in 4general as silica-alumina type catalysts. More particularly, salts of indium and thallium in addition to aluminum in group IIIB may be used, and salts of titanium, zirconium and thorium in group IYA may be used to treat silica gel and to prepare catalysts of this general type. Whether prepared by this method or by some modification thereof, the catalyst will contain a major portion of silica and a. minor portion of metal oxide. This minor portion of metal oxide, such as alumina, will and will more often be between about 0.1 and 1.5 or 2 per cent by weight.

The second stage catalytic treatment for the reduction or olefin and sulfur in the hydrocarbon stream from the aromatization step is preferably carried out as a. liquid-phase operation. 'Depending on the operating temperature, pressures employing Treating temperatures may extend from at- In this manner, a part of the metal, presumably in the form of a hydrous oxide mospheric to about 700 F. depending on the nature of the original feed stock and the extent of purication required to produce a, iinished aviation blending stock. Ordinarily it is preferred to carry out this operation at temperatures of from 200 to about 600 F.

Hydrocarbon ow rates through the treating reactors are necessarily determined to a large extent by the type and quantity of impurities to be removed, the temperature of operation and the activity of the catalyst. Under the conditions of this process ow rates of from 0.5 to 10 liquid volumes per volume of catalyst per hour may be employed although the preferred rates are ordinarily those of 1 to 4 liquid volumes per volume of catalyst per hour.

Catalyst life n the treating stage of this process is ordinarily very long, since the relatively mild conditions coupled with liquid phase operation tend to prevent the accumulation of tai'ry poisons and carbonaceous deposits. Several hundred volumes of material often may be treated with substantial conversion of olen and sulfur impurities to high-boiling constituents before any significant change in catalyst activity is observed.

The nal purification of the aromatic distillates of this process is effected by fractionation of the eiiluent from the catalytic treating chambers. The selective action of the silica-alumina type catalysts converts the residual olefin and sulfur compounds to high boiling derivatives which remain in the kettle product.

In order to illustrate further the speciilc uses and advantages of the present invention, the following exemplary operations will be described. However, since these and numerous other process modifications will be obvious in the light of the foregoing disclosure, no undue limitations are intended.

Example I A cracked gasoline having a 385 F. end point and a gravity of 51.3 API was preheated to a temperature of about 1100o F. prior to aromatization over a bauxite catalyst. A flow-rate of 6 to 8 barrels of feed per ton of catalyst per hour was maintained at a pressure of 85 .pounds gage. The aromatized eil'iuen-t was quenched to separate small quantities of high-boiling material from the gasoline and lighter products and the gasoline was stabilized by the removal of material boiling below about 150 F. The resulting gasoline of 336 F. end point amounted to about 70 per cent of the gasoline charged. The characteristics of the clay-treated product at this stage were as follows:

Sulfur weight percent-- 0.050 Bromine number l Gravity API 45.4 R. V. P p. s. i-- 0.8 3-C blending value, ml., TEL in S reference fuel 1.25

Distillate having the aforementioned properties was preheated to 415-450 F. under a pressure oi 1000 pounds gage in preparation for treatment over a silica-alumina catalyst. The ow rate through the catalyst bed was maintained between 2 to 4 liquid volumes per volume of catalyst per hour and the reaction temperature was not permitted to exceed 500 F. In the subsequent fractionation 94 volume per cent of the distillate having a -335 F. boiling range and the following properties.

Sulfur weight per cent 0.025 Bromine number 7 Gravity API 45.6 Reid vapor pressure p. s. i-- 0.8

3C blending value. ml. TEL in S reference fuel 3.52

Example Il The operation as described herein was carried out substantially as indicated in the drawing to make a benzene concentrate and a 220-345 F. aviation grade fraction.

'I'he charge to the first stage catalytic aromatization was a polyform gasoline of 405 F. end point and a gravity of 50.1 API. The average temperature of the bauxite catalyst bed was maintained between 11501200 F. under a pressure of 85 pounds gage and at a flow rate of about 6 barrels per hour per ton of catalyst. After conventional clay treatment, the eiiluent from the catalyst case was stabilized to remove pentane and lighter constituents. Subsequent fractionations were employed in segregating a crude benzene stream having an ASTM boiling range of 180 F. and an intermediate gasoline fraction with an ASTM boiling range of 200 to 330 F. High-boiling kettle products were recycled to the aromatization reactor along with fresh feed.

Samples of the clay treated product streams exhibited the following characteristics:

Inter Benzene mediate concentrate gasoline fraction Sulfur weight per cent.` 0. 229 0.279 Bromine number 29 l0 Gravity API.. 41.2 3T. l RVP p. s. i.. 3.75 0.95 3-C blending value, mi. PEL i'n S reference fue] 1.34 1.20

Treated products Benzene Inte" mediate cacn' gasoline e traction Sullur weight per cent.- 0. 127 0. 160 Bromine number 8. 0 4. 0 Gravity. API- 41.0 30.8 RVP -p. s. i.- 3. 75 0.85 3-0 blending rating, S+ml. TEL 4. B9 2. 9i Gum, AN-VV-F-781. mg./l00 mi 3. 3 4.8

treated eiuent was taken overhead to yield a u The preceding data emphasize the value of the silica-alumina catalytic treating step of this process in increasing the rich mixture rating of the products with the simultaneous production of a gum stable fuel.

Example III Operation of the process was carried out as described in Example I charging a polyform gasoline of 50.1 API gravity. To obtain comparative data on benefits derived from the clay treatment and the catalytic polymerization operation, 200-330 F. stocks were prepared from the untreated aromatic-containing eiuent, the clay tower product and the product stream from the polymerization treatment. The results are given in the subjolned tabulation.

A gasoline obtained from a polyforming treatment of a straight-run naphtha was topped to prepare a material having the boiling range,.

162-422 F. This feed stock, suitably preheated, was charged to the bauxite catalyst at a rate of 7 to 8 barrels per hour per ton of catalyst. The catalyst chamber was maintained at a pressure of of about 85 pounds per square inch gage and the average temperature of the catalyst bed was about 1150 F. The effluent from the catalyst case was given a conventional clay treatment followed by fractionation to prepare two product fractions as indicated in the subsequent tabulation.

ggg Product rmt-tions Boiling range .F 162-422 150-200 200-350 Sulfur .weight per cent.. 0. 028 0.015 0. 017

Bromine numbe 45 2l 9 Gravity API 47. 6 3-C blending value, ml. TEL in S reference fuel 1.76 3. 32

Because of its relatively high degree of unsaturation as indicated by the above bromine number the 150-200 F. fraction was subjected to further treatment over a silica-alumina catalyst at a temperature of 375-400 F. under a pressure of 1000 pounds gage. The gasoline was fed to the catalyst chamber at a rate of 2 to 3 volumes per hour per volume of catalyst. The catalyst case effluent was fractionated to obtain a product having the following improved properties.

Boiling range F 150-200 Sulfur weight per cent-- 0.009 Bromine number 3-C blending value, ml. TEL in S reference fuel 2.49

Such auxiliary apparatus as valves. flow controllers, pressure measuring or indicating devices, temperature recorders, etc., have not been shown in the drawing nor mentioned in the disclosure for purposes of simplicity and clarity. Such equipment, however, is essential to the successful operation of any process, and the locavvul vll I JU tion, type. operation, etc., of this auxiliary equipment is well understood by those skilled in the art.

It will be realized from the aforegiven explanation and description that many alterations and variations in the apparatus and the operation thereof may be made and yet remain within the intended spirit and scope of our invention.

What we claim as our invention is:

1. A process for the production of improved gasoline stocks comprising passing a cracked gasoline charge stock having a boiling range of approximately to 400 F. in contact with an aromatization catalyst, comprising substantially bauxite, at a temperature of approximately 1050 to 1250 F., at a flow rate of 0.5 to 10 liquid volumes per volume of catalyst per hour, and at a` pressure within the range of about 0 to 200 pounds per square inch gage, separating from the eilluent therefrom a fraction containing hydrocarbons from substantially C5 to about 200 F. boiling point, a fraction containing hydrocarbons boiling from approximately 200 to 350 F., and a fraction boiling higher than approximately 350 F., recycling at least a portion of this latter high boiling fraction into the original charge stock; passing said separated fraction containing hydrocarbons from substantially C5 to about 200 F. boiling point in contact with a polymerization catalyst comprising synthetic silica-alumina, at a temperature within the approximate range of 200 to 600 F. and at a gage pressure within approximately 500 lbs. to 2000 lbs. per square inch, and from the eiliuent of this step separating improved gasoline stocks and a bottoms product boiling at a temperature higher than said improved gasoline stocks and recycling at least a portion of this said higher boiling product into the original charge stock; passing the above separated fraction boiling from approximately 200 to 350 F. in contact with a polymerization catalyst comprising synthetic silica-alumina, at a temperature within the approximate range of 200 to 600 F. and at a gage pressure within approximately 500 lbs, to 2000 lbs. per square inch, and from the eiiluent of this step separating improved aviation gasoline stock boiling from approximately 200 to 350 F. and a liquid bottoms boiling higher than approximately 350 F. and recycling at least a portion oi this latter bottoms with the original charge stock.

2. A process for the production of improved gasoline stocks comprising passing a cracked gasoline charge stock having a boiling range of approximately 150 to 400 F. in contact with an aromatization catalyst, comprising substantially bauxite, at a, temperature of approximately 1050 to 1250 F., at a ow rate oi' 0.5 to 10 liquid volumes per volume of catalyst per hour, and at a pressure within the range of about 0 to 200 pounds per square inch gage, separating from the effluent therefrom a fraction containing" hydrocarbons from substantially C5 to about 200 F. boiling point, a fraction containing hydr carbons boiling from approximately 200 to 350 F., and a fraction boiling higher than approximately 350 F., recycling at least a portion of this latter high boiling fraction into the original charge stock; passing said separated fraction containing hydrocarbons from substantially C5 to about 200 F. boiling point in the liquid state in contact with a polymerization catalyst comprising synthetic silicaalumina, at a temperature within the approximate range of 200 to 600 F. and at a. pressure at least sufficient to maintain said C5 to 200 F. boiling point fraction in the liquid state, and from the eiiluent of this step separating improved gasoline stocks and a bottoms product boiling at a temperature higher than said improved gasoline stocks and recycling at least a, portion of this said higher boiling product into the original charge stock; passing the above separated fraction boiling from approximately 200 to 350 F, in the liquid state in contact with a polymerization catalyst comprising synthetic silica-alumina, at a temperature within the approximate range of 200 to 600 F. and at a, pressure at least sufficient to maintain said C5 to 200 F. boiling point fraction in the liquid state, and from the eiiluent of this step separating improved aviation gasoline stock boiling from approximately 200 to 350 F. and a liquid bottoms boiling higher than approximately 350 F. and recycling at least a portion of this latter bottoms with the original charge stock.

3. A process for the production of improved gasoline stocks comprising passing a cracked gasoline charge stock having a boiling range of approximately 150 to 400 F., in the vapor phase in contact with an aromatization catalyst, comprising substantially bauxite, at a temperature of approximately 1050 to 1250 F., at a flow rate of 0.5 to 10 liquid volumes per volume of catalyst per hour, and at a pressure within the range of about to 200 pounds per square inch gage, separating from the eiiluent therefrom a fraction containing hydrocarbons from substantially C to about 200 F. boiling point, a fraction containing hydrocarbons boiling from approximately 200 to 350 F., and a fraction boiling higher than approximately 350 F., recycling at least a portion of this latter high boiling fraction into the original charge stock; passing said separated fraction containing hydrocarbons from substantially Cn to about 200 F. boiling point in the liquid state in contact with a polymerization catalyst comprising synthetic silica-alumina, at a temperature within the approximate range of 200 to 600 F. and at a pressure at least sufiicient to maintain said C5 t0 200 F. boiling point fraction in the liquid state, and from the effluent of this step separating improved gasoline stocks and a bottoms product boiling at a temperature higher than said improved gasoline stocks and recycling at least a portion of this said higher boiling product into the original charge stock; passing the above separated fraction boiling from approximately 200 to 350 F. in the liquid state in contact with a polymerization catalyst comprising synthetic silica-alumina, at a temperature within the approximate range of 200 to 600 F. and at a pressure at least sufficient to maintain said Cs to 200 F. boiling point fraction in the liquid state, and from the eliluent of this step separating improved aviation gasoline stock boiling from approximately 200 to 350 F. and a liquid bottoms boiling higher than approximately 350 F. and recycling at least a portion of this latter bottoms with the original charge stock.

4. A process according to claim 1 in which the silica-metal oxide catalyst is a synthetic silicaalumina gel containing a, major proportion of silica and a minor proportion of alumina.

5. A process according to claim 1 in which the silica-metal oxide catalyst is a synthetic silicaalumina gel comprising a major proportion of silica and from 0.1 to 2.0 per cent by weight of alumina.

WALTER A. SCHULZE. CARL J. HEIJVLERS. 

